The present invention relates to a shaft tool with a detachable top for metal cutting machining.
Most rotating cutting tools comprise a shaft portion for fixing the tool in a holder and an operative cutting portion comprising cutting edges of a hard material such as cemented carbide, different ceramics, polycrystalline diamond and cubic boron nitride. The cemented carbide may be either coated or uncoated. Usually, the cutting edges consist of one or more of the edge lines on a cutting insert that is fastened upon and constitutes the active, cutting part of the operative cutting portion. This cutting insert is often fastened by a screw, the cutting insert having a through-hole, through which the screw is introduced. In other cases the cutting insert is fastened by a clamp or similar fastening or squeezing element; or by soldering or brazing. Although these well-known fastening arrangements function satisfactorily per se, they are all marred by different inconveniences. Thus, screws and clamps may for instance burst after repeated and/or too strong tightening, or they may sometimes loosen due to vibrations, which in a best case makes necessary a retightening but in a worst case may cause a tool breakdown. Moreover, soldering may cause brittleness and micro-cracks due to the heat when soldering, particularly in the soldered seam. Furthermore, a damaged soldered cutting insert cannot be replaced, wherefore the whole tool has to be disposed of, which of course increases costs. A further disadvantage in connection with locking screws is that it is time-consuming to screw and unscrew locking screws for the fastening of indexable cutting inserts, particularly when there are tens or even hundreds of cutting inserts to be mounted, demounted or indexed.
Tools that are smaller in volume, such as end mills and drills, are usually made integrally of one single piece, whereby they consist of the same hard material as the cutting edges. This brings the advantage that the boundary layer of a screw joint, a clamp joint, a soldered seam, etc, is avoided. On the other hand, this "entirety solution" entails that the expensive and sometimes brittle and heat variation sensible hard material also is present in tool parts where it would not be necessary, for instance in the shaft portion.
Still further fastening arrangements comprise wedges, draw bars, etc.
One drawback in connection with more bulky and material-demanding rotary cutting tools is that each individual tool requires its own material-demanding shaft portion, in spite of the fact that this portion is not worn to the same extent as the operative cutting portion.
Thus, a first object of the present invention is to provide a tool which in first hand is a rotating cutting tool and which comprises a simplest possible fastening arrangement between the shaft portion of the tool and the operative cutting portion.
A second object of the present invention is to decrease the material consumption when manufacturing the tool.
Still another object of the present invention is to lay the basis of a more flexible and polyvalent tool system.